As automobiles have become more complex the number of lights on the rear of the vehicle has become more confusing. In the past some signaling devices have been provided which actuate red, green or amber lights to indicate the intention of the driver. But the prior signaling devices were comparatively complicated, and they relied on lights that were built into the motor vehicle and so they were not suitable for add-on use for vehicles already in service or for attachment to trailers being towed by vehicles.
These devices were often operated by using the accelerator or brake pedal actuated switches causing the various lights in the car to go "on" or "off". Other devices had means for causing an intensification of the brightness in the rear brake lights, to warn following vehicles that the driver has depressed the brakes of his vehicle. Due to the number of lights on the rear of the vehicle, the increase in the intensity of the brake lights when the brakes were applied was not very noticeable, particularly in hazy of foggy weather or when approaching vehicles to the rear were driving into the sun. More recently an additional red light has been mounted at eye level on the rear window of some new cars, but this light is not much of an improvement over the lights on lower rear of these cars for the same reason.